In prior art, wrapping machines for wrapping a round bale are known in which a plastic film is wound around a rotating bale so that, at the end of the wrapping operation, the bale has a plastic film wrapped around it as tightly as possible, the wrapping completely enclosing the bale. The equipment in prior-art solutions includes picking means for picking up a bale from the ground, a wrapping table rotating the bale, a wrapping arm revolving around the bale and provided with a roll of plastic film, a plastic film holder and a plastic film cutter. A known solution is presented in Finnish patent no. 91123, which corresponds to European patent EP0499285.
In previously known solutions, the bale is rotated on a wrapping table about its longitudinal axis in a substantially horizontal position while the wrapping arm, provided with a plastic film roll with a substantially upright axis of rotation, is revolved at the same time about the bale in a horizontal plane. The idea is to surround the bale with a plastic layer as impermeable as possible that will admit no air into the bale. To achieve a sufficiently impermeable layer, at least a four-fold, preferably six-fold plastic layer is needed on the envelope surface of the bale. In addition, the bale is wrapped with individual layers overlapping each other. Due to this known wrapping method, the plastic layers are laid on the bale in the manner shown in FIG. 1. An acceptable layer thickness on the envelope surface of the bale is achieved, but at the same time much too much plastic is accumulated on the end surface of the bale. Especially the central part is covered with as many as 30-40 plastic layers. This means wasting large amounts of expensive plastic. This is one of the drawbacks of prior-art solutions.
Another drawback with known solutions is that there are generally stalks sticking out of the edges of the envelope surface so that the ends of the stalks are pressed against the plastic. The drier the hay is allowed to become before being wrapped, the more damage will the stalk ends inflict on the plastic during wrapping as they stretch the plastic in the stalk end area so that it becomes very thin or is even pierced. Therefore, the total thickness of the plastic layer is not sufficient.
Another disadvantage with prior-art solutions is that, as the volume of the bale is diminished during storage because of fermentation storage loss, the bale shrinks, with the result that the plastic film wrapped longitudinally on the envelope surface becomes loose. The bale volume is reduced during storage by as much as 30% and the bale is deformed at the same time. The plastic layer becoming thinner and loose leads to several problems. First, it permits the entry of air into the bale, increasing fermentation of the fodder and the risk of its contracting mould. In addition, the stretched and slackened plastic on the soft envelope surface of the bale is easily pierced by stubble and other sharp objects on the grassland.